The present invention is directed generally to a sheet inverter. More particularly, the present invention is directed to a sheet inverter useable to invert flexible sheets. Most specifically, the present invention is directed to a sheet inverter for repositioning sheets of flexible corrugated paperboard stock useable in the fabrication of cartons. The corrugated sheets, which are typically printed, scored and slotted, are quite flexible and are positioned on a plurality of spaced belt conveyors which form a sheet stacker. The sheet inverter repositions these corrugated sheets of paperboard by inverting them during their conveyance on the sheet stacker and prior to delivery of the sheets to a sheet stack hopper. The sheet inverting can be accomplished on individual sheets. More typically, a plurality of stacked sheets will be inverted as a group. The sheet inverter utilizes a plurality of sheet inverting fingers which interdigitate with the spaced belt conveyors that support the printed, slotted and scored flexible corrugated paperboard sheets being inverted.
A great number of products are packaged, by their manufacturers, for shipping and distribution in corrugated paperboard cartons or boxes. These corrugated paperboard boxes or cartons are typically supplied to their end user; i.e. the manufacturer of the products to be boxed and shipped, in a non-erected configuration. Clearly, it is not efficient to ship or transport fully set up or erected empty paperboard boxes from the box manufacturer to a product manufacturer, who will then fill these erected corrugated paperboard cartons with his product. Rather, these corrugated paperboard cartons are shipped to the end user in a non-erected configuration. The corrugated paperboard boxes arrive at the end user""s facility each folded flat as a sleeve. Each carton""s bottom and top flaps are usually then folded into place and glued or taped to complete the erection of the cartons immediately before their useage. These non-erected boxes are supplied to the end user by a corrugated box manufacturer.
The corrugated box manufacturer starts with a stack of sheets of corrugated paperboard which he obtains from a supplier of corrugated sheets. The overall size of each sheet has been determined by the box manufacturer or by the end user in accordance with the size of the intended corrugated box or carton. The corrugated paperboard sheets are received by the corrugated box manufacturer from the corrugated sheet supplier typically already provided with across-corrugation score lines. These score lines will, when combined with score lines added by the corrugated box manufacturer, define lines of fold that will typically cooperate with slots cut into the corrugated sheets by the box manufacturer. In some situations, the corrugated sheets received from the supplier are not scored. In those instances, the box manufacturer must score, slot and print the corrugated sheets.
The corrugated sheets are slotted to create the carton""s side panels and end flaps, and are also printed with suitable graphics, as determined by the end user. A machine, typically referred to as a printer-slotter is used for this purpose. The printer-slotter is akin to a rotary printing press and includes one or more pairs of cooperating printing rollers with the number of printing roller pairs being equal to the number of colors that can be printed. The printer-slotter also is provided with multiple pairs of cooperating scoring rollers and slotting knives. The corrugated paperboard sheets are placed, in a stack, on an infeed table of the printer-slotter. As these sheets travel individually through the printer-slotter, each is first printed and scored and is then slotted. The specific graphics printed on the sheets, the location of the slots, the scoring and the cut-outs cut into the sheets can be changed.
The printed, scored and slotted sheets are then fed to an intermediate, driven conveyor, typically referred to as a lay boy. The lay boy accumulates and transfers printed, scored and slotted corrugated paperboard box blanks to a sheet stacker and to a sheet stack hopper for collection and stacking.
A wide variety of printer-slotters are available to corrugated box manufacturers. All can be categorized by the location of their printing plates. They are thus either xe2x80x9ctopxe2x80x9d printers or xe2x80x9cbottomxe2x80x9d printers. The corrugated and now printed, scored and slotted box blanks exit the printer-slotter with their printed surfaces either face up or face down, dependent on the type of printer-slotter which the corrugated box manufacturer may have. Some larger manufacturers may have one or more of either type.
Once the corrugated sheets have been printed, scored and slotted, they are typically placed in a stack by operation of the lay boy, sheet stacker and sheet stack hopper referred to above. These printed and slotted sheets are then formed into non-elected boxes by the folding of each sheet into a sleeve-like configuration. The folded sheets are formed into sleeves by a joining step such as stitching or taping of the sheet ends. After the printed, scored and slotted flexible corrugated paperboard sheets have been formed into these sleeves, they are then again stacked and suitably bound and are then sent to their end user.
The sheets are turned into sleeves by a xe2x80x9cjoiner.xe2x80x9d It is the function of the joiner to fold the sheets along their score lines and to join together the length and width panels of the partially finished box, to form the sleeves. A variety of joiners are available. Some of these form the printed, slotted and scored box blanks into non-elected sleeves by folding the length and width panels of the printed and slotted blanks down and in. Others fold the length and width panels of the blanks up and in. The printed, scored and slotted corrugated sheets provided to a joiner that fold down and in, are supplied with their printed side facing up, assuming that the printed graphics are intended to be situated on the exterior of the folded box. If the joiner folds up and in to form the intermediate sleeve, the printed, scored and slotted blanks must be situated on the joiner with their printed sides facing down.
If only a few printed, scored and slotted corrugated paperboard sheets were to be made into non-erected sleeves, the placement of the printed, scored and slotted sheets on the joiner in a print side up or print side down orientation would be a small task. However, in a corrugated box manufacturing plant, a substantial percentage of each day""s output from the printer-slotter must be inverted to orient them properly for the joining step.
In the past, this inverting step has been done manually or by some makeshift arrangement. The inverting of stacks of sheets, if done manually, is quite likely to cause physical injury. It is a step that frequently requires the participation of two workers, who must leave other tasks to accomplish this one. Such manual sheet inversion places the workers at greater risk of physical injury, with its attendant health and disability costs. It also is very labor intensive and thus increases the cost of the finished product. Since the finished product is a non-erected shipping carton or container, there is a limit to the price that can be charged. All of these factors makes the need for a better, faster, more efficient and less expensive device for inverting flexible sheets of corrugated paperboard, having a wide range of sizes and weights, that much greater.
Several sheet inverting devices are known in the prior art. One of these uses a plurality of arms to invert drywall panels. The arms are provided with large rollers at their free ends. In use, a first group of arms and rollers extend underneath the leading edge of a drywall panel and raise the leading edge. A second set of arms and rollers catch the now trailing edge of the inverted panels and lowers the inverted panels onto the conveyor belt. This system is too slow for efficient use with a printer-slotter in a corrugated paperboard box manufacturing facility. It also depends on the stiffness or rigidity of the sheets to function properly.
Another type of inverting device, which is also intended for use with relatively rigid panels, such as drywall or plywood sheets, uses a group of cantilever arms that are each provided with a downwardly facing hook at their free end. These cantilever arms extend out over the path of travel of the panels. They engage the panel""s leading edge with their hooks, elevate the leading edge of each panel, draw it up and back, and invert each panel as the initially trailing end is conveyed under the raised initially leading end. These devices are again too slow for useage in a relatively high speed application, such as in the inversion of sheets exiting from a corrugated paperboard sheet printer-slotter. In addition, they require a substantially rigid panel for successful operation. Paperboard sheets that have been scored and slotted generally do not have that degree of rigidity.
While the general concept of a panel inverting device is generally known in the art, none of those prior art devices are particularly suitable for accomplishing the inversion of printed, scored and slotted flexible paperboard sheets which are used in the corrugated box industry. The need exists for a sheet inverter that will accomplish the inversion of relatively flexible sheets, such as these printed, scored and slotted corrugated paperboard sheets. Since the overall sizes and weights of the sheets, as well as their conveying speeds vary widely, the device must be able to work at varying conveying speeds and with a variety of sizes and weights of corrugated sheets. It must be efficient, cost-effective, dependable and durable. It must also be adaptable for the cooperative use with other machines in a manufacturing facility and must operate using utilities that are typically available in such a manufacturing facility. The sheet inverter in accordance with the present invention overcomes the limitations of the prior art and provides a device which is a substantial improvement over the prior art.
It is an object of the present invention to provide a sheet inverter.
Another object of the present invention is to provide an inverter for flexible sheets.
A further object of the present invention is to provide a corrugated material sheet inverter.
Yet another object of the present invention is to provide a corrugated paperboard sheet inverter.
Still a further object of the present invention is to provide a sheet inverter that is useable to invert single sheets and stacks of sheets.
Even another object of the present invention is to provide a sheet inverter useable to reposition by inverting printed and slotted flexible corrugated paperboard box blanks.
As will be set forth in greater detail in the description of the preferred embodiment, the sheet inverter of the present invention is intended for use primarily to invert printed, slotted and scored paperboard box blanks that are produced by a printer-slotter. The sheet inverter is intended for use primarily in the corrugated paperboard box manufacturing industry. The printed, scored and slotted sheets exit the printer-slotter and are received by the lay boy in preparation to being forwarded to a sheet stacker. The sheet or stack of sheets are supported on the sheet stacker by a plurality of spaced conveyor belts. The sheet inverter itself utilizes a rotatable shaft that is supported above, and generally transverse to the direction of transport of the sheets. The rotatable shaft is supported at its ends by bearings. A plurality of fingers, at least some of which may be extendable, are attached at first, proximal ends to the rotatable shaft. The second, distal ends of these fingers interdigitate between the spaced conveyor belts. Each finger carries a friction enhancing material on a sheet engaging surface portion of its distal end. Each finger also carries a sheet stop intermediate its ends and adjacent the sheet engaging surface of the distal end. In operation, the sheet or stack of sheets travel along the sheet stacker, engage, and start to climb up the distal ends of the spaced fingers. A double acting pneumatic or hydraulic cylinder is actuated to rotate the shaft and to thereby raise the free, second ends of the fingers up under the forwardly traveling sheet or stack of sheets. This finger elevation, in combination with the continuing forward conveyance of the sheet or sheet stack by the conveyor belts effects an inversion of the sheet or sheet stack. The now inverted sheet or sheet stack travels onwardly on the sheet stacker to a hopper where they accumulate in a stack of sheets that can then be taken to a joiner for further processing.
The sheet inverter in accordance with the present invention, as will be discussed in detail subsequently, works in cooperation with the intermediate lay boy. At higher production speeds of the printer-slotter, as is typical with single thickness corrugated sheets, the sheet inverter could not keep pace with the printer-slotter, assuming that each sheet was inverted individually. Modification of the lay boy or another intermediate conveyor to operate intermittently results in the build-up of a stack of sheets as they come out of the printer-slotter. The sheet inverter of the present invention includes settable controls so that the number of sheets in each stack which is accumulated or built up on the lay boy, before being discharged to the sheet stacker, can be controlled. Depending on the width of each sheet and the operational speed of the printer-slotter, each stack formed on the lay boy can consist of two or more sheets. As stacks of this number of sheets are fed to the sheet inverter, they tend to displace in the direction of travel within the stack. As they are engaged by the free finger ends of the inverter, the inversion process re-aligns the stack.
The sheet inverter of the present invention provides for the control of the speed of elevation and declination of the sheet inverting fingers by controlling the flow of fluid to the chambers of the double acting pneumatic piston or pistons that rotate the shaft which carries the fingers. Again depending on the width, and the speed of travel of the sheet or stack of sheets, the lead time between the start of rotation of the shaft and the arrival of the first leading edge of the first sheet in the stack at the fingers can be controlled. Proper timing is also accomplished by the selection of a suitable rest position of the fingers in their ready position. Clearly this ready position must be one in which the free ends of the fingers are below the surface of the conveyor belts. However, further declination of the free ends of these fingers is not of benefit unless the dwell time of the fingers in their rest position is to be increased. The control arrangement of the speed of rotation of the shaft and its dwell time will insure that the sheet or stack of sheets are inverted and that the fingers are returned to their ready position all in concert with the production speed of the printer-slotter.
The sheet inverter of the present invention is readily adapted to a wide range of sizes of corrugated sheets. As discussed above, the intermittent drive of the lay boy allows the printer-slotter to operate at a higher speed. The control of the rotational speed of the finger support shaft is adjustable to accept sheets of varying widths. Suitable system controls are included to prevent the free ends of the fingers from returning to their ready position too quickly and thus disrupting the exit of the trailing portion of the prior inverted stack of sheets. If the sheets being printed and slotted are quite thick and heavy, thus requiring a slower speed of operation of the printer-slotter, the lay boy can be driven continuously. The sheet inverter can invert each sheet separately, assuming that sufficient time is provided, by operation of the printer-slotter at a low speed.
As discussed previously, printed, slotted and scored corrugated paperboard box blanks, even if arranged in stacks of several blanks or sheets, are relatively flexible. The use of the friction enhancing material on the sheet engaging surface of the free or distal ends of the fingers, together with the proper timing of operation of the sheet inverter, which allows the sheets to be supported by a finite length of each finger, accomplishes the inversion of the sheets despite their flexibility. This is very different from the prior devices that require their panels to be rigid before they can be successfully inverted. The present sheet inverter, while it will also function with rigid panels, such as wallboard or plywood, is primarily intended for use with flexible, corrugated paperboard box materials. As such, it fulfills a unique need in an area of industry which is not addressed by the prior art devices.
The sheet inverter in accordance with the present invention provides a functional, effective solution to the problem created by the need to re-orient printed, scored and slotted corrugated and non-corrugated flexible paperboard box blanks. Operation of the sheet inverter, in conjunction with a commercially available sheet stacker, or other similar sheet handling device, allows a box manufacturer to fully utilize both his printer-slotter and his joiner or joiners without the need for manual intervention in the sheet handling process. The sheet inverter of the present invention is a substantial advance in the art.